The specific aim of this project is to initiate a series of microbeam irradiation studies of isolated RGCs cultured on Mylar surfaces at the RARAF facility. One goal is to be able to perform single hit studies using 90 -240 keV/um a-particles. Various parts of isolated neurons will be hit, with a desired resolution of around 1 to um, and the functional effects of each analyzed. In parallel another goal will be to evaluate if single hits can impair the neuronal viability in culture at different times of culture and differentiation. It is already known that there exists a differential effect of radiation on two aspects of neuritogenesis, neurite formation and elongation suggesting differing mechanisms. The single particle studies are designed to distinguish the vulnerable site for each. An understanding the cellular and molecular mechanisms of the neuronal response to the space radiation environment will provide insights into the adaptive and functional integrity of the nervous system in general. It may also lead to rational strategies for maximizing the nervous system recovery from injury, or to slow the rate of functional deterioration. Together these data are the minimum necessary to predict the consequences of extended space activities on the nervous systems of those whom we send into that environment.